1. Field
The present disclosure relates to an apparatus and associated methods to produce analgesia in a mammal by providing an electrical nerve stimulus utilizing a pulsed input of low level electrical current, wherein the level of current is measurable with the measurements utilized to at least adjust the strength of the current according to selected parameters. Additionally, the use of magnets to produce a magnetic field to further control chronic and acute pain.
2. General Background
Electrotherapy and Pain
There are multiple pharmacologic approaches to the medical treatment of acute and chronic pain. Some of the pharmacologic treatments include acetaminophen, nonsteroidal anti-inflammatory drugs, glucosamine chondroitin, cyclooxygenase-2-selective inhibitors, topical analgesics, and opiate analgesics. Some of the nonpharmacologic options include physical therapy, such as aquatherapy, heat, and aerobic exercises, weight reduction for arthritic pain, bed rest, and osteopathic manipulative treatments.
In the 1960's the medical use of electricity was considered and various physiological rationale were proposed for its electroanalgesic effects. It was observed that chronic pain relief was obtained in some patients when high-frequency percutaneous electrical stimulation was used.
Transcutaneous Electrical Nerve Stimulation Mechanism and Muscle Contraction
Transcutaneous electrical nerve stimulation (TENS) controls pulsed currents delivered through the intact surface of the skin by conducting pads, referred to as electrodes. There are a variety of TENS-like devices available in the market. This proliferation of TENS-like devices has created literature which contains inconsistent nomenclature and ambiguous results in treatment. There are primarily three types of TENS: conventional TENS described herein, acupuncture-like TENS, and intense TENS.
The electrical characteristics of TENS are typically chosen to selectively activate different populations of nerve fibers. In post surgery/disease/injury related physical therapy TENS is used to contract muscles to maintain muscle tone when patients are unable to use the muscles normally. Large diameter nerve fibers (Aβ and Aα) have low thresholds of activation to electrical stimuli when compared to the smaller diameter nerve fibers (Aδ and C). The current amplitude needed to excite a nerve fiber declines as the pulse duration and pulse frequency increases. Therefore one would select low-intensity, high frequency currents with pulse durations between 10 and 1000 microseconds to activate the larger diameter fibers. Conversely increasing the pulse duration will lead to activation of the smaller nerve fibers at lower pulse amplitudes. Manufacturers have introduced features on TENS devices such as modulated amplitude, modulated frequency to assist in controlling muscle response.
TENS is also used to induce analgesia. TENS produces analgesia by a segmental mechanism where the activity generated in the Aβ nerve fibers inhibit ongoing activity in the second-order nociceptive, i.e., pain related, neurons in the spinal cord's dorsal horn.
Transcutaneous Electrical Nerve Stimulation and Pain
Transcutaneous electrical nerve stimulation is a simple non-invasive technique that is used in health care settings by nurses, physiotherapists, and other health-care professionals. TENS is defined by the American Physical Therapy Association as the application of electrical stimulation to the skin for pain relief.
Nadler (2004) in a review of nonpharmacologic treatments indicated that TENS treatment caused about a 50% reduction in pain as opposed to a placebo response.
Maurer et al. (U.S. Pat. No. 4,431,002) and Holcomb (U.S. Pat. No. 6,741,889) indicated that pain relief could occur when electrical pulses were applied to the surface of the body or to electrodes which were implanted within the body. These TENS apparatuses provide electrical nerve stimulus where the stimulus pulses were modulated in both time and intensity in a prescribed manner.
TENS can activate different populations of nerve fibers. Low thresholds of activation to electrical stimuli have been found for the large diameter nerve fibers (Aβ and Aα) when they are compared to nerve fibers, Aδ and C (smaller diameter). As the pulse duration and pulse frequency increases, the amount of current amplitude which is needed to excite a nerve fiber decreases. To activate the larger diameter fibers such as Aβ and Aα typically one would select low-intensity, high frequency currents wherein the pulse durations are between 10 and 1000 microseconds. At lower pulse amplitudes the smaller diameter nerve fibers are activated with an increased pulse duration. Features such as modulated amplitude, modulated frequency, and duration have been introduced on TENS devices.
Conflicting reports have been published about the efficacy and the duration of a TENS application. Factors which contribute to these conflicting reports include (1) stimulus variables not controlled, (2) effect of different electrode placements, (3) dependent on patient's response, and (4) no means of measuring the electrical current applied to the locale undergoing treatment. It is difficult to predict the nature and the distribution of the currents when they pass across the surface of the skin due to the impedance of the tissue. Thus, at present the evidence for TENS effectiveness for chronic pain is inconclusive.
All publications, including patents, published patent applications, scientific or trade publications and the like, cited in this specification are hereby incorporated herein in their entirety.